I. Field of the Invention
The present invention relates to logic drivers. More specifically, the present invention relates to a programmable logic driver circuit for implementation in automatic test equipment wherein the logic driver circuit includes overcurrent protection circuitry.
II. Background Art
Automatic test equipment (ATE) systems are currently used in testing electronic assemblies and subassemblies at various stages in the manufacturing process. For the testing of digital electronic equipment, the ATE system usually incorporates a logic driver for providing logic states to the unit under test. The ATE system in exercising the unit under test provides predetermined logic states as an input to the test unit. The ATE system then monitors the responses of the unit under test to the predetermined inputs. The response data is used in determining whether the unit under test contains a component or manufacturing related defect.
Logic drivers previously used in ATE systems have been linear-type drivers which utilize linear feedback overcurrent protection circuits. When an electrical short occurs at the output of these types of logic driver, due to a defect in the unit under test, the driver momentarily provides a high current output until the overcurrent condition is detected by the driver's overcurrent protection circuit. Once the overcurrent condition is detected the overcurrent protection circuit regulates the driver output current at a constant predetermined maximum value. During the overcurrent condition the drive output current is typically higher than the maximum operating current of the driver. Therefore, significant power dissipation occurs during the overcurrent condition. Accordingly, the driver output elements must be capable of handling, on a continuous basis, higher power outputs. In addition, larger capacity heat sinks must be used for the output elements.
It is, therefore, an object of the present invention to provide a novel and improved programmable logic driver with overcurrent protection which features low power dissipation and high speed operation.
It is yet another object of the present invention to provide a switching logic driver for ATE systems which operates in a switching mode and uses cutoff current limiting protection to achieve minimum power dissipation and component count.
It is yet a further object of the present invention to provide a programmable logic driver with reduced heat sinking requirements and low power driver output components.